Lower cost high strength single crystal superalloys with reduced re and ru content

ABSTRACT

A first embodiment of a nickel based alloy consists essentially of from 3.0 to 5.2 wt % chromium, from 1.5 to 3.0 wt % molybdenum, from 6.0 to 12.5 wt % tungsten, from 5.0 to 11 wt % tantalum, from 5.5 to 6.5 wt % aluminum, from 11 to 14 wt % cobalt, from 0.001 to 1.75 wt % rhenium, from 0.2 to 0.6 wt % hafnium, up to 0.05 wt % yttrium, up to 3.0 wt % ruthenium, and the balance nickel. Another embodiment of a nickel based alloy consists essentially of from 1.0 to 3.0 wt % chromium, up to 2.5 wt % molybdenum, from 11 to 16 wt % tungsten, from 4.0 to 8.0 tantalum, from 5.7 to 6.5 wt % aluminum, from 11 to 15 wt % cobalt, from 2.0 to 4.0 wt % rhenium, from 0.2 to 0.6 wt % hafnium, up to 0.05 wt % yttrium, up to 3.0 wt % ruthenium, and the balance nickel.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. provisional patentapplication No. 61/118,714, filed Dec. 1, 2008, entitled Lower Cost HighStrength Crystal Superalloys With Reduced RE and RU Content.

STATEMENT OF GOVERNMENT INTEREST

The Government of the United States of America may have rights in thepresent invention as a result of Contract No. N00019-02-C-3003 awardedby the Department of the Navy.

BACKGROUND

Lower cost high strength single crystal superalloys with reduced rheniumand ruthenium content are described.

All second and higher generation nickel-base directionally solidifiedand single crystal superalloy compositions contain additions of rheniumof at least 3 wt %. Fourth generation and higher single crystal alloyscontain some percentage of the element ruthenium. With the significantescalation of spot prices of these elements, there is an economic needfor alternate alloy compositions with comparable levels of performance,but with reduced concentration of these expensive elements.

Nickel-base superalloy single crystals are primarily used for hightemperature turbine components, such as blades and vanes, wheretemperature capability is typically assessed by its high temperaturecreep resistance. Simplistically, it is well understood that to improvecreep resistance, additions of refractory elements with high meltingpoint is desirable. Such elements include almost all Group IVA to VIIIAtransition metals, especially Ti, Nb, Ta, Mo, W, Re, and Ru with meltingpoints in excess of 4082° F. (2250° C.). Among these elements, Ti, Nb,and Ta are known to almost exclusively replace Al in the orderedprecipitate phase γ′ (Ni₃Al), whereas Re and Ru are known to exclusivelypartition to the nickel base solid solution γ-matrix. W on the otherhand is known to partition evenly between the γ-matrix and γ′ phase.

There are of course limits to the extent to which these elements can beaccommodated in the alloy. It is common knowledge that optimummechanical properties are obtained when the volume fraction of the γ′phase is around 60 to 70%. Thus, individually or combined (Al+Nb+Ta+W/2)in atom % cannot exceed about 18%. Moreover, Al concentrations cannot bereduced below 10 atom % to preserve oxidation resistance. Similarlyexcessive addition of refractory elements in the γ-matrix is limited bythe undesirable phases these elements can form after a long timeexposure. The formation of so-called topologically closed packed (TCP)phases are undesirable as they reduce the creep resistance of the alloy.The concentration at which such phases will form can be approximatelypredicted by calculating, what is called an electron vacancy number orNv number for the γ-matrix. This calculation is based on a weighedaverage of Nv assigned to each element. It is an industry wide practiceto use such calculations, but it is known that it is not completelyaccurate and there are exceptions to the rule.

There is a need for a lower cost high strength nickel based superalloy.

SUMMARY

A first embodiment of a lower cost high strength nickel based alloybroadly comprises from 3.0 to 5.2 wt % chromium, from 1.5 to 3.0 wt %molybdenum, from 6.0 to 12.5 wt % tungsten, from 5.0 to 11 wt %tantalum, from 5.5 to 6.5 wt % aluminum, from 11 to 14 wt % cobalt, from0.001 to 1.75 wt % rhenium, from 0.2 to 0.6 wt % hafnium, up to 0.05 wt% yttrium, up to 3.0 wt % ruthenium, and the balance nickel.

Another embodiment of a lower cost high strength nickel based alloybroadly comprises from 1.0 to 3.0 wt % chromium, up to 2.5 wt %molybdenum, from 11 to 16 wt % tungsten, from 4.0 to 8.0 tantalum, from5.7 to 6.5 wt % aluminum, from 11 to 15 wt % cobalt, from 2.0 to 4.0 wt% rhenium, from 0.2 to 0.6 wt % hafnium, up to 0.05 wt % yttrium, up to3.0 wt % ruthenium, and the balance nickel.

Other details of the lower cost high strength nickel based superalloys,as well as objects and advantages attendant thereto, are set forth inthe following detailed description and the accompanying drawings whereinlike reference numerals depict like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of tantalum weight % vs. tungsten weight %; and

FIG. 2 is a bubble chart of Ta weight % vs. tungsten weight % with thebubble size proportional to (Re+Ru) weight %

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The combinations of compositions with the elements Ti, Nb, Ta, Mo, W,Re, and Ru along with primary elements Ni, Co, Cr, and Al, is so largethat it is cost prohibitive to explore the entire alloy space.Traditionally, alloys are evolved based on prior experience and once thetarget performance benefit is realized, there is little motivation tovisit the unexplored alloy compositional space. There is no simplequantitative way to map out a space bounded by a dozen elements andpinpoint the gaps. In a limited sense, a bubble plot of Ta weight % vs.W weight %, as shown in FIG. 1, graphically represents maps out adesirable space. In this plot, the size of the bubble or plotting pointfor each alloy is proportional to the total concentration of (Re+Ru) inthe alloys of interest.

Prior to the development of the first generation single crystal alloyPWA 1480, the best known equiaxed and columnar grain alloys were basedon Mar M200, which contain 12.5 weight % of W. Also the alloy contained2.0 weight % Ti. Development of PWA 1480 was marked by the addition of12 weight % Ta. Subsequent development of second generation singlecrystal alloys such as PWA 1484 all had a marked absence of Ti. Animproved second generation DS alloy, PWA 1426, was developed with Readditions similar to PWA 1484. The fourth generation of single crystalalloys such as PWA 1497 have an increase in Re concentration concurrentwith Ru additions. As can be seen in FIG. 1, these alloys do not overlapin the Ta, W, (Re+Ru) space. In these higher strength alloys, theconcentration of Ta never decreased below 4 wt % and W never increasedbeyond 6.0 wt %.

The successful development of second generation single crystal alloyshas been attributed to Re additions and it is generally believed that Remakes the lattice misfit between the γ′ precipitate and the γ-matrixbecome more negative. Re is also thought to reduce the coarsening rateof the γ′ phase, contributing to improving creep strength.

Useful alloys are listed in Table I and are also depicted in FIGS. 1 and2. FIG. 1 clearly depicts that in Ta weight % vs. W weight % plots,current production alloys are outside the alloy space. The Ta inproduction alloys is showed by the diamond points 10 on FIG. 1 and thespace with the Ta in the alloys set forth herein are shown by thesquares in the space 12. The same information is plotted in FIG. 2 as abubble chart, where the size of plotting points is proportional to theconcentration of (Re+Ru). In FIG. 2, bubble 20 is alloy PWA 1422, bubble22 is alloy PWA 1480, bubble 24 is alloy PWA 1497, bubble 26 is alloyPWA 1484, bubble 28 is alloy 2a in Table I, bubble 30 is alloy 2b inTable I, bubble 32 is alloy 1a in Table I, bubble 34 is alloy 1b inTable I, bubble 36 is alloy 3a in Table I, bubble 38 is alloy 3b inTable I, bubble 40 is alloy 3c in Table I, bubble 42 is alloy PWA 1426,bubble 44 is alloy PWA 1426a, and bubble 46 is alloy PWA 1426b.

TABLE I Alloy Cr Mo W Ta Al Co Re Ru Hf P Density Creep Life NV3BStability COMMENTS Single Crystal 1a 4 2 11 6 6 12.5 0 0 48.5 0.322 PWA1484 2.07 S Creep = 1484 No Re/Ru 1b 5 2 9 6 6 12.5 0 3 48.5 0.318 PWA1484 2.07 S Creep = 1484 No Re (3Ru) 1c 4 2 9 6 6 12.5 1.5 0 48.5 0.32PWA 1484 2.04 S 2a 2 1.75 11.5 6 6 12.5 3 3 58 0.331 PWA 1497 2.02 SCreep = 1497 with 3Re, 3Ru 2b 2 1 12.5 6 6 12.5 3 0 55.75 0.331 1497-15F2.02 S Creep~1497 with 3Re, 0Ru 3a 2 1.75 15.5 6 6 12.5 0 3 58 0.334 PWA1497 2.09 S Creep = 1497 with 0Re, 3Ru 3b 2 2 13.5 6 6 12.5 1.5 0 55.250.331 1497-20F 2.08 S creep < 1497 with 1.5Re, 0Ru 3c 2 2 15 6 6 12.5 00 54.5 0.331 1497-25F 2.08 S creep < 1497 with 0Re, 0Ru PWA 1484 5 1.95.9 8.7 5.65 10 3 0 48 0.323 2.08 PWA 1497 2 1.8 6 8.25 5.65 16.5 6 3 580.331 DS PWA 1426 6.4 1.7 6.4 4 5.9 12.5 3 0 1.5 44.9 0.316 Base 2.07 SPWA 1426a 6.4 1.7 8.4 4 5.9 12.5 1.5 0 1.5 44.9 0.318 Base 2.11 S creep= 1426 1.5Re PWA 1426b 6.4 1.7 10.4 4 5.9 12.5 0 0 1.5 44.9 0.322 Base2.24 Mg creep = 1426 0Re

Listed in Table I are baseline compositions of the second and fourthgeneration single crystal alloys PWA 1484 and PWA 1497, respectively,and the second generation columnar grain (DS) alloy PWA 1426. It can beseen from FIG. 2 that using the useful alloys described herein, one canachieve the same level of creep resistance as PWA 1426, for reducingRe-containing alloys (PWA 1426a and PWA 1426b), by increasing the Wcontent of these alloys.

One embodiment of a useful alloy contains from 3.0 to 5.2 wt % chromium,from 1.5 to 3.0 wt % molybdenum, from 6.0 to 12.5 wt % tungsten, from5.0 to 11 wt % tantalum, from 5.5 to 6.5 wt % aluminum, from 11 to 14 wt% cobalt, from 0.001 to 1.75 wt % rhenium, from 0.2 to 0.6 wt % hafnium,up to 0.05 wt % yttrium, and the balance nickel.

Table II is a comparison of alloys having compositions within theaforesaid range with Rene N5. The data shows the alloys described hereinto have higher density, an equivalent or better life, better yieldstrength, and equivalent or better ultimate tensile strength than ReneN5.

TABLE II Casting Chemistry Weight % Act lbs/cu in 1850 F/38 ksi 1200 FTensile Cr Mo W Ta Al Co Re Hf Density Life 1% EI YS UTS EI Alloy 1 3.972.07 10.82 6.07 6.15 12.81 0 0.32 0.320 40.2 16 38.1 124.5 140.2 22 31.710 23.4 124.8 139.1 23.1 37.5 16 25.6 126.2 139.3 24.2 AVE 36.5 14 29125.2 139.5 23.1 Alloy 2 3.99 2.03 8.81 6.01 5.78 12.23 1.54 0.34 0.32061.7 24 28.4 135.8 143.5 21.8 63.1 24 39.3 130.1 137.9 19 68.6 26 36.9130.7 139.1 21.8 AVE 64.5 24.7 34.9 132.2 140.2 20.9 Alloy 3 5.09 2.0910.97 5.62 6.15 12.9 0 0.36 0.319 48.7 16 41.3 120.6 139 17.8 45.5 1438.3 127.3 145.4 17.2 40.6 13 37 127.6 147.2 21.1 AVE 44.9 14.3 38.9125.2 143.9 18.7 Alloy 4 5.01 2.08 9.41 7.04 5.9 12.45 0 0.35 0.320 41.214 36 130.2 145 21.9 41.1 14 37.2 134 150 21.3 42.8 14 41.7 133.3 146.320.9 AVE 41.7 14 38.3 132.5 147.1 21.4 Alloy 5 3.93 2.06 8.87 9.03 5.8912.38 0 0.34 0.323 39.6 10 40.1 132.2 144.7 13.5 38.6 9 35.9 137.7 149.625.6 43.4 13 37.4 134.9 146.9 22 AVE 40.5 10.7 37.8 134.9 147.1 20.4Alloy 6 5.04 2.1 11.82 5.65 5.58 12.46 0 0.34 0.323 40.1 17 29.9 138.1152.7 18.9 40.1 14 26.1 140.8 154.1 23.2 39.6 15 24 139.5 154.9 23.2 AVE39.9 15.3 26.7 139.5 153.4 21.8 Alloy 7 4.51 2.06 7.08 10.07 5.8 12.841.43 0.33 0.3235 66.6 26 42.3 148 179.6 9.3 65.2 25 39.4 148.2 179.212.6 59.9 20 36 149.6 181 7.8 AVE 63.9 23.7 39.2 148.6 179.9 9.9 Alloy 85.08 2.05 8.81 7.32 6.14 12.85 0 0.34 0.317 35.8 11 41.7 129.8 148.315.8 37.2 12 40 129.4 148 16.8 39.4 14 41.8 128.2 145.4 18.4 AVE 37.512.3 41.2 129.1 147.2 17 Rene N5 Nom 7 1.5 5 6.5 6.2 7.5 3 0.15 0.31240.5 122 145

A second embodiment of a useful alloy contains from 4.0 to 5.0 wt %chromium, from 1.7 to 2.3 wt % molybdenum, from 7.0 to 12.5 wt %tungsten, from 5.5 to 10 wt % tantalum, from 5.6 to 6.25 wt % aluminum,from 11.5 to 13.5 wt % cobalt, from 0.001 to 1.75 wt % rhenium, from 0.2to 0.4 wt % hafnium, from 0.001 to 0.01 wt % yttrium, and the balancenickel.

A third embodiment of a useful alloy contains from 1.0 to 3.0 wt %chromium, up to 2.5 wt % molybdenum, from 11 to 16 wt % tungsten, from4.0 to 8.0 tantalum, from 5.7 to 6.5 wt % aluminum, from 11 to 15 wt %cobalt, from 2.0 to 4.0 wt % rhenium, from 0.2 to 0.6 wt % hafnium, upto 0.05 wt % yttrium and the balance nickel.

A fourth embodiment of a useful alloy contains from 1.5 to 2.5 wt %chromium, from 0.5 to 1.5 wt % molybdenum, from 11.5 to 13.5 wt %tungsten, from 5.0 to 7.0 tantalum, from 5.8 to 6.25 wt % aluminum, from11.5 to 13.5 wt % cobalt, from 2.5 to 3.5 wt % rhenium, from 0.2 to 0.4wt % hafnium, from 0.001 to 0.01 wt % yttrium, and the balance nickel.

The above alloys may contain up to 3.0 wt % ruthenium. The total rheniumand ruthenium content of each of the alloys may be no greater than 6.0wt %.

Oxidation resistance can be maintained by the addition of at least 15-30ppm yttrium or other equivalent active elements such as Ca, Mg, andother rare earth elements. Previously, yttrium and other rare earthadditions have not been added to alloys containing elevated levels of W,i.e. greater than 6.0 weight %.

The alloys described herein can fulfill the low cost requirements. SinceRe and Ru raw material prices have risen in the last few years, reducingtheir concentration in new alloys by 50% or more (compared to existingsecond generation and higher alloys) will have a significant effect onmaster heat cost.

It should be apparent that there has been provided in accordance withthe present disclosure lower cost high strength single crystalsuperalloys with reduced rhenium and ruthenium content. While thesuperalloys have been described in the context of specific embodimentsthereof, other unforeseeable alternatives, variations and modificationsmake become apparent to those skilled in the art having read theforegoing description. Accordingly, it is intended to embrace thosealternatives, modifications, and variations as fall within the broadscope of the appended claims.

1. A nickel based alloy consisting essentially of from 3.0 to 5.2 wt %chromium, from 1.5 to 3.0 wt % molybdenum, from 6.0 to 12.5 wt %tungsten, from 5.0 to 11 wt % tantalum, from 5.5 to 6.5 wt % aluminum,from 11 to 14 wt % cobalt, up to 1.75 wt % rhenium, from 0.2 to 0.6 wt %hafnium, up to 0.05 wt % yttrium, up to 3.0 wt % ruthenium, and thebalance nickel.
 2. The nickel based alloy of claim 1, wherein saidchromium is present in an amount from 4.0 to 5.0 wt %.
 3. The nickelbased alloy of claim 1, wherein said molybdenum is present in an amountfrom 1.7 to 2.3 wt %.
 4. The nickel based alloy of claim 1, wherein saidtungsten is present in an amount from 7.0 to 12 wt %.
 5. The nickelbased alloy of claim 1, wherein said tantalum is present in an amountfrom 5.5 to 10 wt %.
 6. The nickel based alloy of claim 1, wherein saidaluminum is present in an amount from 5.6 to 6.25 wt %.
 7. The nickelbased alloy of claim 1, wherein said cobalt is present in an amount from11.5 to 13.5 wt %.
 8. The nickel based alloy of claim 1, wherein saidrhenium is present in an amount from 0.001 to 1.75 wt %.
 9. The nickelbased alloy of claim 1, wherein said hafnium is present in an amountfrom 0.2 to 0.4 wt %.
 10. The nickel based alloy of claim 1, whereinsaid yttrium is present in an amount from 0.001 to 0.01 wt %.
 11. Thenickel based alloy of claim 10, wherein the total ruthenium and rheniumcontent is no greater than 6.0 wt %.
 12. A nickel based alloy consistingessentially of from 1.0 to 3.0 wt % chromium, up to 2.5 wt % molybdenum,from 11 to 16 wt % tungsten, from 4.0 to 8.0 tantalum, from 5.7 to 6.5wt % aluminum, from 11 to 15 wt % cobalt, from 2.0 to 4.0 wt % rhenium,from 0.2 to 0.6 wt % hafnium, up to 0.05 wt % yttrium, up to 3.0 wt %ruthenium, and the balance nickel.
 13. The nickel based alloy of claim12, wherein said chromium is present in an amount from 1.5 to 2.5 wt %.14. The nickel based alloy of claim 12, wherein said molybdenum ispresent in an amount from 0.5 to 1.5 wt %.
 15. The nickel based alloy ofclaim 12, wherein said tungsten is present in an amount from 11.5 to13.5 wt %.
 16. The nickel based alloy of claim 12, wherein said tantalumis present in an amount from 5.0 to 7.0 wt %.
 17. The nickel based alloyof claim 12, wherein said aluminum is present in an amount from 5.8 to6.25 wt %.
 18. The nickel based alloy of claim 12, wherein said cobaltis present in an amount from 11.5 to 13.5 wt %.
 19. The nickel basedalloy of claim 12, wherein said rhenium is present in amount from 2.5 to3.5 wt %.
 20. The nickel based alloy of claim 12, wherein said hafniumis present in an amount from 0.2 to 0.4 wt %.
 21. The nickel based alloyof claim 12, wherein said yttrium is present in an amount of from 0.001to 0.01 wt %.
 22. The nickel based alloy of claim 12, wherein the totalruthenium and rhenium content is no greater than 6.0 wt %.